The CP farm is a problem and GW did try and fix it with this new BIG FAQ2, but they aren't there yet.. Farming is now somewhat dammed in but getting the easy high CP battalions/brigades especially how Guard can do it to supplement other Imperial armies is still not addressed.
I like how Tapletop Tactics explained it in their vox cast
https://www.youtube.com/watch?v=i8PsXwS6aTYAs for the play-ability, I really like it.. 8th was for me the way to get in and not drown on all the crap 7th brought with it. And yes the Stratagems are a nice addition to work with to make armies stand out more and give them some hidden/special possibilities, but it would work better if high end Stratagems would not be so easy to use, like 3-4 time in a battle giving you a certain edge int he battle where the opponent can't really recover from (looking at you Castelan Knight)
I wish cover mattered more, getting first turn meant less and facing actually meant something
Getting 2nd turn now gives you a 2cp Stratagem that rewards a Cover save for all models that didn't already have it (excluding Titanic models), so getting first turn does matter less. I think T'au actually benefits from it more. And having last turn for objective grabbing might turn the game in your favour also.
I can't really comment on the amount of HQ able to field / required to field.. I'm only used to 8th and for me with T'au I find it ok, even with the Commander keyword limitation to 1 per detachment.